Sign up to workflow using a field change trigger

I plan to send an email to my current email list to give them an option to opt in for a series of email, which I will send out with automation. My question is how can I do it? Do I put a link on the email for them to sign up for the automated email and if so, how to do it? thank you.

Yes, that's definitely possible, and there are a few steps involved in getting this setup. Essentially, you'll want to have contacts fill out a signup form (manage preferences form), where they can indicate if they want to receive the series of emails -- then, you'd setup a field change workflow, and that will only trigger to contacts who have said yes to receiving that series. For your convenience, I've outlined the full steps below, with links to the related Resource Center articles:

1. Create a new contact field: Create a new contact field called "Do you want to opt into the series emails?", for example, and that'll be a radio button with the options "Yes" and "No".

2. Signup form: Create a new classic signup form titled "Workflow signups", and only include/require the "Do you want to opt into the series of emails?" question (since email address will automatically be included on the form). Be sure to add those subscribers to a new, specific "Opt into workflow" group. Also, on the "Manage preferences email" tab, uncheck the box that sends a confirmation email. Here's what that signup form would look like (when a subscriber clicks on the link from your email):

3. Email to current subscribers: In your mailing to current subscribers, you can add a button block, and add the following to the button's link section: [% manage_url %]. Then, on that mailing's "Review & Send" page, be sure to change the signup form to your newly created "Workflow signups" form. This way, when any contact clicks the button block, they will be brought to the signup form seen above, and their email address will already be populated.

4.Field Change Workflow: Create a new workflow and choose your "Opt into workflow" group as the audience. The trigger event will be a field change, and you'll select the "Do you want to opt into the series of emails?" question from the list. Then, set it up so the workflow triggers when that question's answer changes from "empty" to "Yes" -- which means, if someone clicks "Yes" on the signup form page, they would receive that workflow.

I know there were a few steps involved with this, but it's a tested method, so you'll be golden from here :)

Of course, just let me know if you have any follow-up questions for me!